Re: Videos not playing in this Yahoo site

Your problem is caused basically by the way Yahoo lays out the movie: until it's started, it hides it under its own placeholder (hence you can't see NoScript's).
Also, if you click Yaohoo's placeholder, NoScript "senses" the click because it's in the same position as its own hidden placeholder and enables the Flash player.
Unfortunately, though, the player remains hidden under Yahoo's placeholder and you can't see it. Furthermore, if you click again the click is delivered to the player, but since it is concealed by Yahoo's placeholder and it's cross-site, you (rightly) get the ClearClick warning.

Finally, even if you reload the page after allowing the swf player (either from the hidden placeholder or from the "Blocked objects" submenu) Yahoo changes the movie parameters, hence the player gets blocked again as it was delivering a different movie, and you're back at square one.
The only work around is using the "Blocked objects" submenu in order to allow *@http://l.ytimg.com.

Fortunately this is not gonna happen for most people, because unless you've got the Apply these restrictions to whitelisted sites as well option set everything will work smoothly.